Many automotive vehicles have rear wheel drive. Additionally many automotive vehicles with rear wheel drive have selective four wheel drive capabilities which are actuated upon operator command or automatically actuated in response to a slip condition of the powered rear wheels of the vehicle. To provide four wheel drive capabilities in the vehicle, there is provided a transfer case. The transfer case is typically provided at an output of the vehicle's transmission. Referring to FIGS. 1-4, the transfer case 7 often has an outer housing provided by front shell and rear shell 12. In many transfer case designs, a front axle gear (not shown) is supported in the front and rear shells and rotates about a secondary axis. The front axle gear is torsionally connected with a front axle differential of the vehicle. An idler or intermediate gear 42 is supported by the housing. The intermediate gear is meshed with the front axle gear. A main input shaft 30 rotates about a coaxially aligned primary axis generally parallel to the secondary axis. The main input shaft 30 is rotatively supported by the front shell and rear shell 12. The main input shaft 30 is torsionally connected with an output shaft of the transmission of the vehicle and with a rear axle (via a prop shaft and rear differential) of the vehicle. A main sprocket gear 50 is provided that is rotatably mounted on the main input shaft 30. The main sprocket gear 50 is meshed with the intermediate gear 42. A clutch mechanism is provided to selectively torsionally connect the main sprocket gear with the main input shaft.
To lubricate the bearings supporting the main input shaft and a friction pack 12 of the clutch mechanism there is provided a gerotor pump. The intermediate gear 42 powers the gerotor pump. In many transfer case applications, the rear shell 12 is a casting. An interior of the rear shell is machined for placement of a roller bearing 46 to support a rear end of the intermediate gear 42. An exterior portion of the rear shell is machined to provide a fluid intake or inlet port 31 for the gerotor pump 41. Concentric with the inlet port of the gerotor pump, the exterior of the rear shell is machined for acceptance of inner 43 and outer 47 rotor gears of the gerotor pump. A central bore is provided connecting the interior and exterior of the rear shell 12 for receipt of a shaft 52 connected with the intermediate gear 42 to power the gerotor pump. An exterior of the gerotor pump 41 is sealed by a cover plate 49 that is boltably connected to the rear shell. An outlet port 51 of the gerotor pump feeds into an external lubrication tube 53. The external lubrication tube re-enters the rear shell connecting with a passage 57 of the rear shell that delivers lubricant to a portion of the main input shaft that has a radial passage, allowing for lubricant to enter into a central bore 59 of the main input shaft. The lubricant enters the main input shaft adjacent an area of the main input shaft that is supported by the rear bearing 46 and then exits the main input shaft through another radial passage to lubricate a clutch mechanism 63 of the transfer case.
A factor that can contribute to the cost and or reliability of the transfer case is that the rear shell of the transfer case is machined from an interior side for mounting the bearing 46 supporting the intermediate gear 42, then is also machined from the exterior side to provide an inlet port and for a section supporting the inner and outer rotors 43,47 of the gerotor pump. Additional costs are incurred to ensure the concentricity of the portion of the rear shell that is machined from the exterior side versus the portion of the rear shell machined from the exterior side. It is desirable that all required machining for the lubrication pump be from one side of the rear shell. Another challenge is that the inlet port is typically directly machined into the rear shell exterior side. If the transfer case 7 is being utilized on various vehicles with different lubrication requirements, it is often desirable to slightly modify the radial position of the inlet port and thus there can be a requirement for a customized machining of the rear shell for the different vehicles. It is desirable provide a transfer case design wherein the inlet port of the gerotor pump can be modified without requiring different machining operations in the rear shell.
As mentioned previously, the aforementioned transfer case design requires a cover plate to seal the gerotor pump in the rear shell. The cover plate must be secured by bolt fasteners and the cover plate must be sealed. In some applications the fastener bolts must additionally be sealed. Still another challenge of the aforementioned transfer case design is the cost and installation of an external lubrication tube 53. The ends of the external lubrication tube must be sealed and are also subject to a pull test during assembly to ensure proper installation. It is desirable that the external lube tube be eliminated from the design. Still another factor to consider is the stiffness of the rear shell in the area of the rear shell supporting the rear bearing supporting the main input shaft. It is desirable that this aforementioned area of the rear shell be as stiff as possible.